The present invention relates to methods and apparatus for manipulating cable during an anchor chain retrieval operation, and more particularly, to apparatus and methods which enable cable spooling operations to be simultaneously performed during an anchor chain or cable retrieval operation thereby minimizing delay in the overall offshore operation.
Anchor chains or cable moorings are typically used to provide lateral anchoring support for offshore rigs in deep water operations. When the operator desires to move the rig, it is necessary to retrieve the anchoring chains or cable moorings and this operation, typically is time consuming. The anchor chains, at the anchor end of the chain typically has a short length of buoy cable connected to an underwater buoy and a pendant cable extending between the underwater buoy and a surface buoy. In the retrieval operation, to bring the anchor chain onto the rig, a boat is used. The boat operation involves bringing the floating surface buoy aboard the boat and attaching the pendant cable to the anchor-handling-winch.
The anchor-handling-winch then retrieves the cable on the boat and raises the anchor from the sea-bed to permit recovery of the anchoring chain to the rig.
The present invention concerns itself with handling and storage of the pendant cable while the anchoring chain is being recovered by the rig so that as soon as the anchor chain is fully recovered on the rig, the boat is in condition to begin the next recovery operation of an anchoring chain without further delay. By storing the cable on spools on the boat, the cable is protected against damage which might occur if the cable is left lying in loops or loose on the deck.
In accord with the present invention, a boat is provided with an empty anchoring handling winch. The boat is positioned in the water relative to the surface buoy which is attached by pendant cable to an underwater buoy and to the underwater anchor at the end of an anchor chain. The surface buoy is then brought onto the boat deck.
The pendant cable attached to the anchor is made in at least two segments, the lower segment being attached between the anchor on the sea floor and cloverleaf ring containing three connecting apertures or openings. Two of the apertures are connected to ends of the upper and lower pendant cables and the other aperture is connected to the underwater buoy. The empty anchor handling winch on the boat is used to spool the upper pendant cable onto a reel on the boat while lifting the anchor from the floor of the body of water. When the underwater buoy is retrieved on the deck of the boat, the underwater buoy is disconnected. A towing cable, which is located on the towing winch is attached to the aperture on the cloverleaf ring. Once the towing cable is attached to the cloverleaf ring, and the weight of anchor and chain is taken on the towing cable, the pendant cable can be disconnected from the cloverleaf ring. The anchor is then in a relatively fixed depth position in the water while the anchor chain or mooring cable is reeled into the drilling rig. During the period of time that the anchor chain is being retrieved on the drilling rig, the pendant cable end which had been previously attached to the cloverleaf ring is attached to a vertical, empty storage reel which is located to one side of the boat. After connection of the cable, the storage reel is driven to spool the pendant cable from the anchor handling winch to the storage reel. After the pendant cable is entirely wound onto the storage reel, a davit means is used to reposition the storage spool from a vertical spoling reel spindle to another location on the boat deck. Thus, another empty reel can be placed on the spooling reel spindle and together with the empty reel on the anchor-handling-winch on the deck, the boat is then ready to repeat the recovery operation for anchor chain retrieval.
In many instances, the pendant cable comes in such great length that it is interconnected in segments and thus a segment of the cable can be spooled onto the anchor-handling-winch and unspooled while the towing cable holds the remainder of the pendant cable in suspension. Thus, each of the segments can be spooled independently of one another during the time period that the anchor chain is being retrieved. There are significant advantages, of course, in being able to spool the pendant cable on reels such as protecting the cables from damage and preventing coils of cable on the deck. It also facilitates storage of these cables while the boat is moved.